1. Field of the Invention
The present invention relates to a panel member for an automobile, particularly relates to a panel member for an automobile preferably used in an automatic two-wheel vehicle or an automatic four-wheel vehicle.
In addition, the present invention relates to a panel fastening method for roll-fastening a plurality of panels and a panel structure applied with the panel fastening method.
2. Related Art
In a background art, there is used a hemming structure of overlapping an outer panel and an inner panel and folding to bend a flange formed to erect at a hem portion of the outer panel to pinch in the inner panel at a hem portion of a panel member for an automobile of a bonnet, a trunk and a door or the like of an automobile.
For example, JP-A-2003-170741 describes a panel member of a door for an automobile in which a hem portion of an outer panel is fastened to a hem portion of an inner panel by folding to bend the hem portion of the outer panel to pinch in the hem portion of the inner panel.
FIG. 25 is a vertical sectional view cutting a hem portion of a panel member for an automobile according to a constitution of the background art in a plate thickness direction. In this case, as shown by FIG. 25, by further folding to bend a hem flange 100b of an outer panel 100 preparatorily bent substantially in an L-like shape, a front face 102a of an inner panel 102 is pinched in to fasten to thereby constitute a hem portion.
However, according to the constitution of FIG. 25, the inner panel 102 is only pinched in by the hem flange 100b of the outer panel 100 to fasten and therefore, there is concern of a deficiency in a fastening strength, and there is a case in which the deficiency in the strength is compensated for by also using an adhering agent, spot welding or the like. Further, in order to avoid a problem that the front end face 100a of the outer panel 100 is rusted by being exposed to outside, it is necessary to coat a seal member 104 of a dust sealer or the like (refer to FIG. 25). Therefore, there are needed a step of coating an adhering agent, a step of carrying out spot welding and a step of coating the seal member 104 and the like to pose a problem that a number of fabricating steps is increased.
Further, in bending to fasten a hem portion of a panel member requesting a three-dimensional shape having a number of radii of curvature at the hem portion as in a panel member for an automobile, in order to prevent a wrinkle from being brought about after having been fastened, only a hem flange of the portion of the radius of curvature needs to be smaller than a hem flange at other portion. Therefore, at a portion having a radius of curvature, for example, at a corner portion as shown in FIG. 26, in folding to bend the portion, a force in a direction indicated by an arrow mark of FIG. 27 is operated and therefore, a wrinkle is liable to be produced, there is not a method of dealing therewith other than shortening the hem flange 100b of the outer panel 100 at the corner portion, and the portion is inferior in view of an outlook thereof.
Furthermore, the portion of folding to bend the outer panel 100 is operated with a force in an arrow mark B direction in FIG. 25 (a direction widening from RO portion), the folded-to-bend portion is slightly rounded, so-to-speak sagging is brought about by increasing a radius of curvature RO and therefore, there poses a problem that the outlook is further deteriorated.
Further, JP-A-07-124653 describes that after a hemming step of folding to bend a hem portion of an outer panel to thereby pinch in a hem portion of an inner panel to fasten, there is carried out an after hem step of subjecting a hemmed portion formed by the hemming step to spot welding. The after hem step is carried out with an object of reinforcing a bonding strength of the hemmed portion.
FIG. 28 is a partially omitted vertical sectional view for explaining a panel structure fastened by the background art method. In this case, first, by further folding to bend a hem flange portion 300b including a front end face 300a of an outer panel 300 which has been preparatorily bent substantially in an L-like shape, a front end face 302a of an inner panel 302 is pinched in to fasten.
Successively, a hem portion fastened as described above is welded by a spot welding gun 304 (after hem step), at this occasion, when a strike mark or a thermal strain by the spot welding gun 304 remains at an outer surface 300c of the outer panel 300, an outlook of a product is deteriorated. Hence, at this occasion, a back bar 306 (lower die) in line with a shape of the outer surface 300c is brought into contact therewith, and welding is carried out in a state of butting an electrode only to a side of the hem flange portion 300b. 
Meanwhile, according to the background art constitution, welding is carried out only from an upper side of FIG. 28, that is, the side of the hem flange portion 300b (indirect welding) and therefore, a bonding portion cannot be pressed sufficiently, further, a shunt current is liable to be generated and therefore, it is difficult to achieve a sufficient bonding strength.
Further, a facility of a C gun type used in an ordinary spot welding apparatus or the like cannot be used to divert, further, also the back bar 306 matched to the shape of the work is also needed and therefore, there poses a problem that it is difficult to widely use the facility.